1. Field of the Invention
This invention relates to an exhaust brake system installed in a large-size vehicle such as a truck or a bus.
2. Description of the Related Art
A large-size vehicle is equipped with an exhaust brake system which operates in combination with a diesel engine and which has an exhaust brake valve for opening and closing the exhaust passage of the engine.
When the exhaust brake valve is closed, the discharge of gas from the combustion chamber of the engine is restricted, and therefore, the pressure in the combustion chamber rises during the exhaust stroke of the engine. The increased pressure exerts a force upon the piston in a direction to impede the upward motion thereof, that is, to push back the piston, during the exhaust stroke, with the result that the engine itself functions as brake. During operation of the exhaust brake system, injection of fuel into the combustion chamber is automatically suspended.
When the exhaust brake system is rendered inoperative by depression of the accelerator pedal, the exhaust brake valve is opened and at the same time the injection of fuel into the combustion chamber is restarted. Accordingly, the combustion and exhaust strokes of the engine are performed normally, whereby the engine output increases, permitting acceleration of the vehicle.
The exhaust brake system described above is useful in assisting the foot brake of the vehicle, but in some cases, black smoke is temporarily produced and contained in the exhaust gas from the engine immediately after the exhaust brake system is rendered inoperative.
To reduce the generation of such black smoke, Unexamined Japanese Patent Publication No. 3-246343, for example, discloses an exhaust brake system in which the suspension of fuel injection into the combustion chamber is continued until a predetermined time period elapses after depression of the accelerator pedal.
However, if the fuel injection is suspended even though the accelerator pedal is depressed, the engine output cannot be increased, which deteriorates the response to vehicle acceleration, that is, the drivability of the vehicle.